Loans and Allowance for Loan Losses - Average Impaired Loans, Broken out by Portfolio Segment and Class of Financing Receivable (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Financing Receivable, Impaired [Line Items]
Average impaired loans	$ 39,279	$ 30,568	$ 40,719	$ 34,568
Commercial loans
Financing Receivable, Impaired [Line Items]
Average impaired loans	34,987	26,891	36,307	26,449
Consumer loans
Financing Receivable, Impaired [Line Items]
Average impaired loans	4,292	3,677	4,412	8,119
Software
Financing Receivable, Impaired [Line Items]
Average impaired loans	4,306	2,689	4,631	2,040
Hardware
Financing Receivable, Impaired [Line Items]
Average impaired loans	25,456	18,490	24,536	17,407
Venture capital/private equity
Financing Receivable, Impaired [Line Items]
Average impaired loans	75	0	35	0
Life science
Financing Receivable, Impaired [Line Items]
Average impaired loans	0	0	303	78
Premium wine
Financing Receivable, Impaired [Line Items]
Average impaired loans	1,502	3,093	2,458	3,334
Other
Financing Receivable, Impaired [Line Items]
Average impaired loans	3,648	2,619	4,344	3,590
Real estate secured loans
Financing Receivable, Impaired [Line Items]
Average impaired loans	3,426	2,411	3,391	5,967
Consumer loans
Financing Receivable, Impaired [Line Items]
Average impaired loans	$ 866	$ 1,266	$ 1,021	$ 2,152